Tape Automated Bonding (TAB) is a process that is used to interconnect a chip to a package. The TAB process involves bonding an integrated circuit (IC) device to a patterned metal on a polymer tape which typically consists of copper foil on a polyimide tape. Once the IC device is bonded to the tape the apparatus is commonly referred to as a Tape Carrier Package (TCP).
FIG. 1 illustrates the backside of a typical prior art TCP 10 as assembled and tested before it is shipped to a customer. As shown in FIG. 1, the copper on the TCP 10 is patterned to form electrically conductive leads 14 that are used for supplying power, grounding, and exchanging signals between IC device 12 and a substrate, such as a printed circuit board (PCB). Inner leads 14a are bonded to pads (not shown) located on the opposing side of IC device 12. Test pads 16 are also provided along the outer periphery of TCP 10 to facilitate the electrical testing of IC device 12 before the TCP is shipped to the customer. The metallurgy of leads 14 and contact pads 16 typically consists of copper that is gold plated over a nickel flash. Note also that sprocket holes 9 are used to position the TCP throughout the manufacture and assembly processes.
With continuing reference to FIG. 1, outer lead bonding windows 18 represent those portions of the TCP where the polyimide tape 8 has been removed to expose outer leads 14b. Bonding windows 18 are provided to facilitate the bonding of outer leads 14b to the electrical contact pads on a PCB (not shown). As mentioned above, when the electrical testing of IC device 12 is complete the TCP is shipped to the customer. Using specialized equipment the customer trims the TCP along either lines A--A or B--B and subsequently mounts the TCP to a PCB.
Referring to FIG. 2a and FIG. 2b, the TCP of FIG. 1 is shown trimmed along lines A--A and B--B, respectively. During the trimming process outer leads 14b are trimmed as depicted in FIGS. 2a and 2b. Note that test pads 16 are removed and discarded by the customer during the TCP trimming process. After the TCP is trimmed it is reflowed onto the PCB (not shown) by one of several methods including hot bar, hot gas, or laser reflow. In general, the reflow process includes bonding the TCP to the electrical contact pads of the PCB by heating and forcing the outer leads against the solder coated bonding pads of the PCB (not shown). FIG. 3 illustrates the TCP of FIG. 2a after the outer lead bonding procedure is complete. As shown in FIG. 3, outer leads 14b are bonded to pads 23 of PCB 22.
Once a TCP has been mounted to a PCB problems may arise in the performance of the IC device. In these instances the TCP must be removed from the PCB so that the IC device may be tested to verify its performance. In order to remove the TCP from the PCB the TCP outer lead and the PCB contact pad interfaces are heated to reflow the solder connection between the TCP and PCB. The TCP can then be carefully removed from the PCB using one of a number of techniques. One such technique includes the use of a suction device that attaches itself to the TCP and lifts it from the PCB surface. Once removed, the TCP is remounted to either an interposer circuit board, a daughter board, or similar type device, where it undergoes failure analysis testing. Mounting the TCP onto the interposer circuit board requires that each outer lead of the TCP be soldered to corresponding pads on the surface of the board.
As integrated circuits and circuit board technology has improved, substantially greater functionality has been incorporated into modern integrated circuits. In addition, the portability of computing and information management is driving the reduction in size from desktop to laptop to notebook to palm top sized products. These products, such as notebook computing systems, require lightweight small footprint integrated circuits. Consequently, as integrated circuits have expanded in functionality the number of leads required to effectively communicate with these devices has greatly increased while the size of the devices have diminished. For example, Intel Corporation has recently introduced IC devices requiring TCP component packages having outer lead pitches as low as 0.2 mm.
The extremely fine pitch lead devices being fabricated today have made it increasingly more difficult to remove and test the devices after they have been mounted and reflowed onto a PCB. Using even the best of techniques to remove the TCP from a PCB inevitably results in lead damage and shorts between the metal coated leads. As a consequence, many of the leads must be repaired and individually realigned before they are remounted to an interposer circuit board for failure analysis testing. Moreover, the mounting of a TCP onto an interposer circuit board requires that each outer lead of the TCP be soldered to corresponding pads on the surface of the interposer board. This procedure is labor intensive and requires that personnel be specially trained in the attachment process. More importantly, since it is difficult to verify the integrity of each lead attachment to the interposer board, the reliability of the failure analysis test is compromised. In fact, in those instances where the outer leads have received extensive damage during the removal of the TCP from the PCB, the testing of the IC device may be precluded altogether using current post mount testing techniques.
Another problem associated with current TCP designs involves the location of test pads 16 as depicted in FIG. 1. As clocking frequencies continue to increase the ability to test IC devices has become increasingly more difficult because of the electrical switching noise that results from the high speed switching operations of the IC device. Having test pads 16 located at the outer periphery of TCP 10 contributes to the switching noise problem by effectively maximizing the impedance between the test pads and the IC device.
What is needed then is a solution to the problems inherent in the prior art. As will be seen, the present invention provides an improved TCP that solves the aforementioned problems.